Short answer: An older edition can be fine for stable basics such as anatomy structure, but check key topics against a current source because guidelines and drug information change.
Know what changes and what does not
Basic structure and many core concepts change slowly. Guidelines, treatment approaches, classification systems and drug information change more often. Treat these parts of an older book with caution.
The preface of the newer edition usually lists what was updated. If you can see it, use it as a checklist.
Compare with a current source
Borrow a current copy from a friend, a senior or the library and compare the chapters you rely on. Look at the contents page and a few key topics to see how they differ.
If the new edition has added chapters or reorganised topics, note which pages in your copy are no longer enough.
Ask your department
Your teachers know which edition they use for questions and which parts of older editions are still valid. A quick question can save you from studying outdated material.
For exams, check the recommended edition in your syllabus or university notice before you decide.
Practical tips
Keep a short list of topics where you know your copy is outdated. Share it with classmates who use the same edition so that you can all update together.
If you decide that the older edition is not enough, a current copy can be shared with a friend or bought. Weigh the cost against how much of the book you will actually use before you decide.
Quick checklist
Check the preface of the new edition, compare key chapters, ask your department, mark doubtful parts and update them from a current source. Do this at the start of the term, not before the exam.
Doing it early gives you time to fix gaps calmly, and leaves the last weeks for revision.
Mark uncertain parts and update them
Use sticky notes or pencil to mark sections that may be outdated. Update them using a current source, and write the date of the update.
Medical books are expensive, so many students compare options on second hand books and new books. Read more in do new editions matter for medical textbooks.
In clinical subjects, treat any dose, protocol or classification in an older book as something to verify. Your notes for exams can still use the book's explanations, but confirm the specific values against a current source before you rely on them.
Frequently asked questions
Is an older edition of a medical textbook safe to study from?
It can be for stable basics, but verify guidelines, drug details and classifications against a current source.
How do I know what changed in the new edition?
Check the preface or contents page, or compare chapters with a current copy.
Should I follow my teacher's edition?
Yes, especially for exams. Your department can tell you which edition to use.